So-called open clamps made from band material, usually galvanized steel or stainless steel, which utilize a plastically deformable "Oetiker" ear for tightening the clamp have been commercially available and highly successful for many years. Before tightening the clamp by plastic deformation of the "Oetiker" ear, the overlapping band portions must be mechanically connected, for example, by spot-welding or preferably by one or more hook-shaped members in the inner of the overlapping band portions engaging in one or more apertures in the outer overlapping band portion. One or more so-called guide hooks, sometimes also called suspension hooks, which are bent out of the clamping band about a transverse axis after a substantially U-shaped cut in the longitudinal direction of the clamping band, have been used for many years for that purpose. FIGS. 1 through 3 illustrate a so-called open clamp with such a guide hook 21 extending obliquely outwardly from the inner band portion 11b and engaging in one of several apertures 22 in the overlapping outer clamping band portion 11a, as disclosed in U.S. Pat. No. 3,321,811. Though the present invention is theoretically applicable to any tightening device which requires a mechanical connection before tightening can be commenced, it is of particular significance and advantage when used with open clamps that are tightened by plastic deformation of a so-called "Oetiker" ear generally designated in FIG. 1 by reference numeral 13 and consisting of generally outwardly extending parallel leg portions 14 and 15 interconnected by a bridging portion 16, normally provided with a reinforcing groove or pan-shaped depression (not shown) as described, for example, in U.S. Pat. No. 5,282,205. The problem encountered with the prior art mechanical connections using only one such guide hook 21 was the likelihood of reopening of the mechanical connection in the course of the application of tightening forces which cause the hook 21 to bend back into a clamp re-opening position 21' (FIG. 3). To reduce the likelihood of reopening of the clamp owing to a bent-back guide hook, a combination of a guide hook 31 and deep-drawn support hook(s) 32 was proposed for such clamps in U.S. Pat. No. 4,299,012, whereby upon application of tightening forces by plastic deformation of the ear 13, the outer band portion 11a, guided along the inclined surface of the guide hook 31, would be drawn toward the inner band portion 11b to assure engagement of support hooks 32 in their apertures 35 (FIG. 4). In turn, this permits improved absorption of the higher tightening forces by the support hooks. This prior art arrangement proved highly successful. Nonetheless, if the speed of the increase of the tightening forces, for example, with the use of pneumatic tools, exceeds a certain value, depending also on clamping band material, thickness of the clamping band and length of the guide hook determining the lever arm, it may happen that the guide hook bends back before the overlapping band portions have come close enough to one another to cause engagement of the support hooks in their respective apertures.
Such open clamps are made from flat steel band material and are usually deformed into more or less circular shape to facilitate installation over the hose and engagement of the guide hook in its aperture before tightening can be commenced by plastic deformation of the "Oetiker" ear. However, such predeformation is likely to cause spring stresses to be set up in the clamping band which seek to return the clamping band to a more straight configuration, i.e., seek to reopen the clamp by disengagement of the outer band portion 11a from the guide hook. Thus another pre-existing problem was the likelihood of reopening when the outer band portion 11a slides again outwardly over the edge of the free end of the guide hook under the spring forces. This danger is the greater the shorter the guide hook. On the other hand, the longer the guide hook, the greater the lever arm seeking to bend the hook into the guide-hook reopening position. To counteract these contradictory effects, it has been proposed heretofore to bend the free end of the guide hook as shown at 21a in FIG. 5. This improves the problem but does not completely eliminate the same.